Water absorbing polymer

ABSTRACT

A process for producing a substantially dry polymer particle powder. A mixture of polymerization reagents is formed from a mixture of at least one monomer source and a solvent selected from the group consisting essentially of water and organic solvents and an initiator source. The mixture of polymerization reagents is sprayed into a heated, controlled atmosphere, forming droplets of the mixture which are allowed to fall through the heated, controlled atmosphere for a sufficient period of time to obtain a desired degree of polymerization. The solvent is continuously evacuated from the atmosphere during the polymerization process.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a spray polymerization process,an apparatus for producing a dry polymer and a polymer having novelphysical characteristics. Particularly, the present invention relates toa polymerization process for the continuous production in a controlledatmosphere of a substantially dry polymer particle powder comprisingpolymer particles of desired size, shape and density from a liquidmonomer source.

[0002] It is known in the art that polymers may be synthesized by steppolymerization and chain polymerization processes. Chain polymerizationis initiated by a reactive species produced by a compound or compoundsreferred to as an initiator. Generally, monomers show varying degrees ofselectivity with regard to the type of reactive center that will causechain polymerization. Monomers show high selectivity between anionic andcationic initiators, however, most monomers will undergo polymerizationwith a radical initiator, although at varying rates. Examples of thetypes of monomers which will polymerize to high molecular weightpolymers in the presence of a radical initiator include: ethylene;1,3-dienes; styrene; halogenated olefins; vinyl esters; acrylates;methacrylates; acrylonitrile; methacrylonitrile; acrylamide;methacrylamide; N-vinyl carbazole; N-vinyl pyrrolidone.

[0003] Essentially, radical polymerization conditions are eitherhomogenous or heterogeneous, depending upon whether the initial reactionmixture is homogenous or heterogeneous. Some homogeneous systemshowever, may become heterogeneous as polymerization proceeds due to theinsolubility of the polymer in the reaction media. Generally, mass andsolution polymerizations are homogeneous processes, while suspension andemulsion polymerizations are heterogeneous processes. All monomers canbe polymerized by any of the various processes however, it is usuallyfound that for commercial considerations the polymerization of aparticular monomer is best carried out by one or two of the processes.

[0004] Bulk or mass polymerization of a pure monomer offers the simplestprocess with a minimum of contamination of the product. Bulkpolymerization, however, is difficult to control due to thecharacteristics of radical chain polymerization. The bulk process ishighly exothermic, high activation energies are involved, and there is atendency toward the gel effect. Such characteristics make thedissipation of heat difficult, therefor, careful temperature control isrequired during bulk polymerization processes. Additionally, theviscosity of the reaction system increases rapidly at a relatively lowconversion, thereby requiring the use of elaborate stirring equipment.Localized “hot spots” may occur which damage, degrade and discolor thepolymer product, and a broadened molecular weight distribution mayresult due to chain transfer between polymer molecules. There is alsothe risk in extreme cases that an uncontrolled acceleration of thepolymerization rate can lead to disastrous runaway-type reactions.

[0005] Many of the disadvantages of bulk polymerization may be overcomeby polymerizing a monomer in a solvent (solution polymerization). Thesolvent, which may be water, acts as a diluent and aids in the transferof the heat of polymerization. The solvent can be easily stirred sincethe viscosity of the reaction mixture is decreased. Although thermalcontrol of a solution polymerization process is easier than with mass orbulk polymerization, the purity of the polymer may be affected if thereare difficulties in removing the solvent during and followingpolymerization.

[0006] Heterogeneous polymerization is used extensively to control thethermal viscosity problems often associated with homogeneous processes.Precipitation polymerization is a heterogeneous polymerization processwhich begins as a homogeneous polymerization but converts toheterogeneous polymerization. A monomer either in bulk or in solution(usually aqueous but sometimes organic) forms an insoluble polymer inthe reaction medium. Precipitation polymerization can be referred to aspowder or granular polymerizations because of the forms in which thefinal polymer products are obtained. The initiators used inprecipitation polymerization are soluble in the initial reaction mediumand polymerization proceeds following absorption of monomer into thepolymer particles.

[0007] Suspension polymerization, also referred to as bead or pearlpolymerization, is carried out by suspending the monomer (discontinuousphase) as droplets (50 to 500 μm in diameter) in water (continuousphase). The ratio of water to monomer typically will vary from about 1:1to 4:1 in most polymerizations. The monomer droplets which aresubsequently converted to polymer particles do not coalesce due toagitation and the presence of suspension stabilizers also referred to asdispersants or surfactants. Stabilizers may be water soluble polymers orwater insoluble inorganic powders. The suspension stabilizers are usedtypically in an amount that is less than 0.1 weight percent of theaqueous phase. The two-phase suspension system cannot be maintained insuspension polymerization without agitation.

[0008] Suspension polymerization initiators are soluble in the monomerdroplets and are referred to as oil-soluble initiators. Suspensionpolymerization in the presence of high concentrations of water solublestabilizers are used to produce latex-like dispersions of particleshaving small particle size. Such suspension polymerizations may bereferred to as dispersion polymerizations. Inverse microsuspensionpolymerization involves an organic solvent as a continuous phase of awater soluble monomer either neat or dissolved in water. Inversedispersion refers to systems involving the organic solvent as continuousphase with dissolved monomer initiator that yield insoluble polymer.

[0009] Emulsion polymerization involves the polymerization of monomersin the form of emulsions, i.e., colloidal dispersions. Emulsionpolymerization differs from suspension polymerization in the type andsmaller size of the particles in which polymerization occurs, in thekind of initiator employed, and in the dependence of polymer molecularweight on reaction parameters. For most polymerization processes thereis an inverse relationship between the polymerization rate and thepolymer molecular weight. Large decreases in the molecular weight of apolymer can be made without altering the polymerization rate by usingchain transfer agents. Large increases in molecular weight can be madeonly by decreasing the polymerization rate, by lowering the initiatorconcentration, or lowering the reaction temperature.

[0010] Emulsion polymerization allows increasing the polymer molecularweight without decreasing the polymerization rate. Emulsionpolymerization has the advantage of being able to simultaneously obtainboth high molecular weights and high reaction rates. The dispersingmedium is usually water in which the various components are dispersed bymeans of an emulsifier. Other components include the monomer, adispersing medium and a water soluble initiator. Surfactants aretypically used in emulsion polymerizations at from 1 to 5% weight. Theratio of water to monomer is generally in the range 70/30 to 40/60 byweight.

[0011] The polymerization processes discussed above involve additionalsteps either to dry the polymer formed, separate the polymer from theorganic solvent used in the process, or to recover the organic solvent.The added steps require additional energy and time in preparing thefinal product, thereby increasing the cost of the polymer produced.Moreover, the polymers produced using these known processes typicallyare produced as an agglomeration which must, following drying, bepulverized or in some way broken up to yield a usable polymer product.Breaking up the polymer product by grinding or pulverizing produces asubstantial amount of dust which raises environmental and healthconcerns to those having to work in and around the polymer dust.

[0012] Therefore, there remains a need for a polymerization process andan apparatus in which to carry out the process which will enable theproduction of a dry polymer particle powder, thus eliminating the needto dry and pulverize the polymer product produced. There is also a needfor a polymerization process for producing polymers which areimmediately available for use following the completion of thepolymerization process.

[0013] Finally, there is a need for a process to produce a polymer whichallows the size, shape, and density of the polymer to be controlledeasily and precisely. This is particularly important, for example, withpolymers used in situations where a smooth surface is beneficial, suchas in fiber optic cables. Fiber optic cables, which are becoming morecommon in telecommunications, are susceptible to invasive water.However, the use of super-absorbing polymers in fiber optic cables isproblematical because of the relatively “soft” cladding around eachfiber. The “softness” of the cladding makes it prone to scratching,which alters the refractive index of the cladding, and therefore, theability of the fiber to conduct light. Experimentation has shown thatsuperabsorbers produced by known processes cause very fine scratching ofthe cladding, an effect which is attributed to the rough surfaces of thepolymer particles resulting from the pulverization, grinding, orchopping of the solid cross-linked polymer resulting from theabove-described production methods into a fine powder as describedabove. The scratches in the surface of the cladding occur whenever thefiber optic cable is flexed, e.g., when the cable is wound on a spooland then wound off the spool for installation.

[0014] Polymerization processes frequently require that polymerizationtake rate or on a nucleating particle of some kind. For example, U.S.Pat. No. 4,135,043 discloses a process for manufacturing hydrophilicpolymers. A previously formed polymer is coated with similar typemonomers to form a coating on the polymer seed. Thereafter, the coatedseed is heated in order to polymerize the coating thereon. Processes ofthis type also require that the additional production steps discussedabove be employed.

[0015] Exemplary shortcomings of current polymerization processes arethe known methods for the production of water-absorbing polymers. Suchmethods can be categorized as involving either an aqueous system or amulti-phase process. Aqueous systems for production of such polymersgenerally result in a semi-solid mass of material from which water mustbe removed in an energy-intensive drying step. For instance, in U.S.Pat. No. 4,295,987, the mixture of polymerized monomers must bedehydrated with excess methanol to form a firm solid that is dried in,for instance, a vacuum oven, and then ground into particles of a desiredsize or into a powder.

[0016] Also known are methods for continuous production of such polymersin an aqueous system as illustrated by the description set out in U.S.Pat. No. 4,525,527, hereby incorporated in its entirety by this specificreference thereto. Briefly, that patent describes the heating of anaqueous monomer solution to which an initiator is added by pouring theinitiator onto the mixture as the mixture flows onto a travelingconveyer belt. The polymerization is exothermic, helping to drive offthe water, and results in a “relatively dry, solid polymer of low watercontent”, said to be 8-15% water. The solid polymer is then made into apowder by pulverization.

[0017] Multi-phase processes involve polymerization of an aqueousreaction mixture in an inert organic solvent, followed by the removal ofthe solvent from the polymerized product. So far as is known, suchprocesses are batch processes, and a representative example of such aprocess in U.S. Pat. No. 4,446,261, hereby incorporated in its entiretyby this specific reference thereto. That patent describes thepreparation of polymer beads by suspension of an aqueous solutionmonomer and crosslinker in a hydrocarbon or halogenated aromatichydrocarbon and polymerization of the monomer upon addition of a watersoluble initiator. As described in that patent, the hydrocarbon isremoved by distillation under reduced pressure and the residual polymerparticles dried by heating under reduced pressure.

[0018] Other examples of such processes are found in the following U.S.patents: AQUEOUS 3,661,815 3,669,103 4,071,650 4,167,464 4,286,0824,295,987 4,342,858 4,351,922 4,389,513 4,401,795 4,525,527 4,552,9384,612,250 4,618,631 4,654,393 4,703,067 MULTI-PHASE 4,059,552 4,093,7764,340,706 4,446,261 4,459,396 4,666,975 AQUEOUS/MULTI-PHASE 4,062,8174,654,039

[0019] Both types of processes are characterized by a number ofdisadvantages which add to the cost of producing such polymers such thatthere is a need for an improved method for producing these and otherpolymers. For instance, both aqueous and multi-phase batch processesrequire drying of the polymer.

[0020] Another disadvantage to producing polymers by knownpolymerization methods, particularly with respect to water-absorbingpolymers, is the difficulty often experienced in controlling the size,shape, and density of the polymers produced. For example,water-absorbing polymer particles with a smooth external surface are, sofar as is known by Applicants, are previously unknown. It appears thatat least some multi-phase methods for production of such polymers resultin spherical (see, for instance, column 5, lines 39, 48 and 60 of theabove-incorporated U.S. Pat. No. 4,446,261) or donut-shaped (see column6, line 57 of the above-incorporated U.S. Pat. No. 4,342,858) particles,but Applicants have been unable to find any such particles which have asmooth surface. Instead, all known particles are characterized by eithera rough surface or by a surface such as that described in theabove-listed U.S. Pat. No. 4,342,8 (column 6, lines 56-58) as being“high surface area donuts of collapsed spherical shapes with 2 to 5micron protuberances on their surfaces”.

[0021] Some additional disadvantages are characterized at, for instance,column 2, lines 56 et seq. of U.S. Pat. No. 4,093,776 and column 1,lines 18-56 of U.S. Pat. No. 4,625,001, both hereby incorporated intheir entirety by this separate reference thereto.

[0022] It is, therefore, an object of the present invention to provide anovel polymer in which the size, shape and density of the polymer can beeasily and precisely controlled, and a process and apparatus for doingso.

[0023] It is another object of the present invention to provide a novelpolymer in which the degree of crosslinking and the water content of theresulting particle can be conveniently and precisely controlled, and aprocess and apparatus for doing so.

[0024] It is an object of the present invention to provide a novelpolymer which is not formed on a substrate or other precursor which actsas a seed or nucleus for the polymer formation, and a process andapparatus for doing so.

[0025] It is an object of the present invention to provide a process andapparatus for producing a polymer which eliminates the difficultyinherent in the handling of the highly viscous solution, gel, or cakeresulting from the production of such polymers with known processes.

[0026] It is another object of the present invention to eliminate thenecessary grinding, pulverization, and/or chopping of a semi-solid massof polymer which characterizes known processes for making polymers.

[0027] It is another object of the present invention to eliminate thecostly step of recovering the organic solvent or medium used in knownprocesses for the production of polymers.

[0028] Another object of the present invention is to provide a processand apparatus for producing a polymer which eliminates the costly dryingstep of many known processes for producing polymers.

[0029] It is an object of the present invention to provide apolymerization process which allows the polymerization reaction, polymerparticle size, polymer particle shape, and water content of the polymerparticle powder produced to be easily controlled.

[0030] It is an object of the present invention to provide a process andapparatus for using a fluid source of a selected monomer to produce asubstantially dry polymer particle powder.

[0031] Other objects, and the advantages, of the present invention willbe made clear to those skilled in the art from a review of the followingdetailed description of the presently preferred embodiments thereof.

SUMMARY OF THE INVENTION

[0032] An atmospheric chain polymerization process is provided. Theprocess comprises preparing a first mixture of at least one monomersource and a solvent selected from the group consisting of water,organic solvents and mixtures thereof, and adding an initiator source tothe first mixture to form a second mixture of polymerization reagents. Acrosslinker, neutralizer, or other reagents may also be added to thefirst mixture. The mixture of polymerization reagents is sprayed into aheated, controlled atmosphere. The heated, controlled atmosphere ismaintained in a closed vessel, such as a reaction chamber. Spraying themixture results in the formation of droplets which experience free fallthrough the heated, controlled atmosphere for a sufficient period oftime to obtain a desired degree of polymerization. The solvent iscontinuously evacuated from the atmosphere during the polymerizationprocess.

[0033] It is preferred that the mixture of polymerization reagents issprayed into the chamber at the top section of the chamber. It is alsopreferred that the reaction chamber is about 3.65 to about 30.48 metersin height. Preferably, the pressure in the reaction chamber ismaintained at less than ambient atmospheric pressure. Desired pressurelevels include from about 338.6 to about 50,790 N/m² below ambientatmospheric pressure. Further, it is preferred that the reaction chamberis heated to a temperature of from about 23.8° C. to about 148.8° C.during the polymerization reaction.

[0034] It is further preferred that the first mixture is maintained at adesired temperature and pressure prior to adding the initiator source.It is also preferred that the second mixture is maintained at atemperature of between about 26.6° and about 93.3° C.

[0035] In the preferred embodiment of the process, the second mixture ofreagents is sprayed into the atmosphere through one or more nozzles. Asubstantially dry polymer particle powder is produced by thepolymerization reaction. Polymer particle is defined herein as asubstantially dry powder-like product. Substantially dry means that theparticles will not agglomerate or stick together, and the powder is freeflowing. The present process enables the production of polymers fromabout 20 microns to about 125,000 microns in size. However, polymersize, shape, and density in a powder will be fairly uniform whenprepared under similar pressure, temperature, and the other parameterswhich will be more fully discussed in the Detailed Description of theInvention.

[0036] The size of the polymer particle produced may be varied byincreasing or decreasing the size of the nozzle opening. In thepreferred process the mixture of polymerization reagents is sprayed intothe heated, controlled atmosphere at a pressure of between about 517 KPaand about 13.7 MPa. The dry polymer particle powder may be recoveredwhile maintaining a heated, controlled atmosphere.

[0037] The monomer source may be an aqueous solution, slurry, oremulsion of a selected monomer. The preferred solvent is water.Similarly, the crosslinker source may be an aqueous solution, slurry, oremulsion of a selected crosslinker and the solvent is water.

[0038] Monomer sources which may be polymerized using the processinclude unfunctionalized olefins and functionalized olefins, includingbut not limited to acrylic acid, ethylenes, dienes, styrenes,propylenes, vinyls, methacrylates, acrylonitrile, methacrylonitrile,acrylamide, methacrylamide, and alkenes.

[0039] A polymerization process is also provided for producing anacrylic acid containing polymer. The process comprises the steps ofpreparing an aqueous mixture of partially neutralized acrylic acid,adding a polymerization initiator to the aqueous mixture to form asecond mixture of polymerization reagents, and spraying said secondmixture into a heated, controlled atmosphere. The spraying of themixture results in the formation of droplets of said second mixturewhich are allowed to fall through the heated, controlled atmosphere fora sufficient period of time to obtain a desired degree of polymerizationand thus form a partially neutralized acrylic acid containing polymer inparticle powder form.

[0040] Polymers produced according to the process are also provided.

[0041] A radical polymerization apparatus is provided. The apparatuscomprises a reaction chamber, a means for heating the reaction chamber,preferably from about 3.65 to about 30.48 meters in height, a means forcontrolling the pressure within said reaction chamber, one or morenozzles connected to a feed line for receiving a mixture of a monomersource and an initiator source, and a means for spraying the mixtureinto the top section of the reaction chamber. Spraying the mixture intothe chamber results in the formation of droplets which fall through thereaction chamber for a sufficient period of time to obtain a desireddegree of polymerization. It is preferred that the mixture is sprayedinto the reaction chamber at from about 517 KPa to about 13.7 MPa ofpressure.

[0042] Preferably, the pressure in the reaction chamber is maintained atless than ambient pressure. Desired pressure levels include from about338.6 to about 50,790 N/m² below ambient atmospheric pressure. Further,it is preferred that the reaction chamber is heated to a temperature offrom about 23.8° C. to about 148.8° C. during the polymerizationreaction.

[0043] The apparatus may further comprise a means for removing thepolymer from the bottom of said reaction chamber while maintaining theheat and the pressure within the chamber. The means for removing thepolymer may comprise a trough located in the bottom of the reactionchamber, a first auger mounted in the bottom of the trough for movingthe polymer out of the chamber, a bin into which the first augerdeposits the polymer and a second auger mounted in the bottom of the binfor moving the polymer out of the bin.

[0044] It is preferred that the apparatus further comprises a means forcontrolling the temperature of the monomer and initiator mixture in thefeed line. It is also preferred that the apparatus includes a means formixing the monomer and initiator before it is sprayed into the chamber.

[0045] Means are also provided for removing unpolymerized monomer in avapor state from said reaction chamber by purging the reaction chamberwith nitrogen. Separate reservoirs are provided for the monomer sourceand the initiator source. Reservoirs may also be provided for acrosslinker source, and other reagents. When it is desired thatcrosslinked polymer structures be produced, crosslinker is added to themixture of monomer source and initiator source prior to the mixturebeing sprayed into the reaction chamber.

[0046] Polymers produced using the apparatus may be polymerized fromunfunctionalized olefins and functionalized olefins, including but notlimited to acrylic acid, ethylenes, dienes, styrenes, propylenes,vinyls, methacrylates, acrylonitrile, methacrylonitrile, acrylamide,methacrylamide, and alkenes.

[0047] A polymer is produced by a radical polymerization processcomprising the steps of preparing a first mixture of at least onemonomer source and a solvent selected from the group consistingessentially of water and organic solvents, adding an initiator source tothe first mixture to form a second mixture of polymerization reagents,then spraying the second mixture of reagents into a heated, controlledatmosphere. The heated, controlled atmosphere is maintained in a closedvessel or reaction chamber which is preferably about 3.65 to about 30.48meters in height. Preferably., the second mixture is sprayed in at thetop section of the vessel.

[0048] It is preferred that the first mixture is maintained at a desiredtemperature and pressure prior to adding the initiator source. It isalso preferred that the second mixture is maintained at a temperature ofbetween about 26.6° C. and about 93.3° C. The spraying of the secondmixture of reagents into the atmosphere through one or more nozzlesresults in the formation of droplets which are allowed to fall throughthe heated, controlled atmosphere for a sufficient period of time toobtain a desired degree of polymerization. The solvent and unpolymerizedmonomer is continuously evacuated from the atmosphere during thepolymerization process. The polymer produced is in dry particle powderform and is recovered from the vessel while maintaining a heated,controlled atmosphere. The polymers may range in size from about 2 toabout 125,000 microns in size. The size of the polymer particle producedcan be varied by increasing or decreasing the size of the nozzleopening. It is preferred that the second mixture of polymerizationreagents be sprayed into the heated, controlled atmosphere at a pressureof between about 517 KPa and about 13.7 MPa.

[0049] In a preferred embodiment, the atmosphere is maintained at atemperature of from about 23.8° C. to about 148.8° C. It is alsopreferred that the controlled atmosphere is at reduced pressuremaintained at a pressure of from about 338.6 to about 50,790 N/m² belowambient atmospheric pressure.

[0050] When desired to produce crosslinked polymer structures, acrosslinker may be added to the first mixture. A neutralizer may also beadded to the first mixture. The monomer source may be a water-soluble,unsaturated monomer which, when a crosslinker is added to thepolymerization mixture of reagents, results in a water-absorbing polymerbeing produced.

[0051] The monomer source may be an aqueous solution, slurry, oremulsion of a selected monomer. The preferred solvent is water.Similarly, the crosslinker source may be an aqueous solution, slurry, oremulsion of a selected crosslinker and the solvent is water.

[0052] The monomer source may be unfunctionalized olefins orfunctionalized olefins, including but not limited to acrylic acid, orselected from the group of compounds consisting essentially ofethylenes, dienes, styrenes, propylenes, vinyls, esters, acrylates,methacrylates, acrylonitrile, methacrylonitrile, acrylamide,methacrylamide, and alkenes.

[0053] An acrylic acid containing polymer is produced by an aqueousradical polymerization process comprising the steps of preparing anaqueous mixture of acrylic acid, adding a polymerization initiator tothe aqueous mixture to form a second mixture of polymerization reagents,and spraying the second mixture into a heated, controlled atmosphere.Spraying results in the formation of droplets of the second mixture. Thedroplets of the sprayed second mixture are allowed to fall through theheated, controlled atmosphere for a sufficient period of time to obtaina desired degree of polymerization and thus form an acrylic acidcontaining polymer in particle powder form. The polymer produced is awater-absorbing polymer in substantially dry powder form and has, forexample, a particle size of less than approximately 100 microns.

[0054] An unexpected advantage of producing polymers in accordance withthe present invention is the production of a particle having a smoothexternal surface, making possible certain new uses for such polymers,particularly water-absorbing polymers. For instance, known waterabsorbing polymers may be used to advantage in telecommunications cablesfor the purpose of protecting the conductors from shorts caused byinvasive water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055]FIG. 1 is a schematic representation of an apparatus constructedin accordance with the present invention.

[0056]FIG. 2 is a sectional view, taken along the lines 2-2 in FIG. 1,of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0057] Referring first to FIG. 1, there is shown an apparatusconstructed in accordance with the present invention designatedgenerally at reference numeral 10. Briefly, the apparatus 10 iscomprised of a reaction chamber or other closed vessel 12, means forheating the reaction chamber 12, shown schematically at referencenumeral 14, means for reducing the pressure in reaction chamber 12 inthe form of the vacuum pump 16, nozzle 18 connected to a feed line 20for receiving a mixture of a monomer and an initiator from therespective sources 22 and 28 thereof, and means, in the form of the binsand auger system indicated generally at reference numeral 26, forremoving the dry polymer particle powder produced in reaction chamber 12from the bottom thereof while maintaining reduced pressure in thereaction chamber 12. Reaction chamber 12 will preferably be about 3.65to about 30.48 meters in height.

[0058] In more detail, the apparatus 10 includes sources, or reservoirs,of monomers 22, initiator 28, and a third reservoir 24 preferablycomprising a source of a crosslinker. A crosslinker or combination ofcrosslinkers will be added to the monomer and initiator mixture when itis desirable to produce crosslinked polymer structures, such aswater-absorbing acrylic family polymers. Other reservoirs (not shown),each preferably individually temperature controlled, are provided forother monomers (for co-polymerization processes), water, neutralizer,stabilizer, transfer agent, solvent, or other reagents.

[0059] Each of the reservoirs 22, 24 and 28 may contain an aqueousand/or organic solvent-based solution, suspension, or emulsion of therespective reagent and therefore is preferably provided with valves 30,32 and 34, respectively, for controlling the flow of the respectivereagents therefrom under the influence of the pumps 36. Alternatively,feed line 20 is pressure fed from the respective reservoirs 22, 24 and28. Feed line 20 is provided with means, indicated generally atreference numeral 44, for mixing the aqueous and/or organicsolvent-based mixture of reagents to insure uniform distribution betweenmonomer, initiator, and other reagents of the polymerization mixture.Mixing means 44 takes a number of forms known in the art such as anin-line screw or auger, mill, vat with stirring blades, or bafflesystem. Also provided is a hatch 38 in the housing of mixing means foradding any other types of reagents.

[0060] Because the polymerization of the monomer begins almostinstantaneously upon the mixing of the initiator and monomer andproceeds rapidly in an exothermic reaction, the temperature of themixture in feed line 20 is used to control the degree of polymerizationof the monomer and, when crosslinkers are added, the degree ofcrosslinking of the polymer structure (note that FIG. 1 is not drawn toscale). To that end, a means is provided for controlling the temperatureof the mixture in feed line 20 which is shown schematically at referencenumeral 42. Temperature control means 42 may take the form of a waterbath, refrigeration coils, insulation, a combination of heating elementsand refrigeration coils, or any other means known for controllingtemperature, depending upon the nature of the monomer(s) beingpolymerized and/or crosslinked. Means 42 is used primarily to reduce theheat resulting from the exothermic polymerization reaction. Lowering thetemperature of the reagent mixture in line 20 prevents thepolymerization rate of the monomer source.

[0061] In a preferred embodiment, line 20 is provided with a nitrogenpure chamber 45 fed by a line 46 having a valve 48 therein for a flow ofnitrogen to purge the mixture of reagents flowing therethrough. Ametered pump 40 in feed line 20 provides control over the pressure andrate of flow of the mixture of reagents.

[0062] The pressure of the atmosphere in reaction chamber 12 iscontrolled during the polymerization reaction. The pressure of theatmosphere in reaction chamber 12 may be reduced relative to the ambientpressure by vacuum pump 16, the atmosphere therein being removed fromreaction chamber 12 through line 50. A filter 52 is provided at theintake of line 50 to prevent droplets/particles of polymerized monomerfrom being pulled into vacuum pump 16. Filter 52 is preferably set in aframe accessible from the exterior of reaction chamber 12 to facilitateperiodic changing of the filter element (not shown).

[0063] The pressure of the atmosphere in reaction chamber 12 may also beincreased above ambient atmospheric pressure in order to produce apolymer particle of a more dense construction than is produced at belowatmospheric pressure.

[0064] An air intake or vent line 54 having a flow control valve 56therein is provided at the top of reaction chamber 12 for allowingambient air into reaction chamber 12 to purge line 50 and pump 16 and/orin the event of an emergency shutdown. Instead of using air intake line54 as a vent, nitrogen can also be introduced into the atmosphere inreaction chamber 12 through line 54 to purge the atmosphere therein, inwhich case, a purge line 55 is provided for recapturing the nitrogen.Again, a filter 57 prevents polymer particles from being pulled intoline 55. Reaction chamber 12 is also provided with means 62, in the formof a clean-out hatch, for removing unpolymerized monomer, or, in theevent of a malfunction of particle removing means 26, the drypolymerized particles, from the bottom thereof. Heater 14 may bemultiple resistive heating elements, gas burners, or steam lines,indicated schematically at reference numeral 58, powered from a commonline 60 from a source of electricity, steam, or gas (not shown).

[0065] Means 26 is provided for removing the polymer from the bottom ofreaction chamber 12 while maintaining the heat and atmosphere therein.Means 26 may be any of the devices known to those skilled in the art.For example, as shown in FIG. 1, a V-shaped trough 64 is formed from twosloping sides 66 which form the bottom of reaction chamber 12. A firstauger, screw, or other continuous conveyer system 68 is mounted in thebottom thereof for moving the particles of polymer out of reactionchamber 12 for deposit into a bin 70. Bin 70 is provided with a secondauger, screw, or other continuous conveyer system 72 mounted in thebottom thereof for moving the polymer deposited therein by first auger68 out of bin 70 into a hopper, bag or other storage/collectioncontainer 74. The respective augers 68 and 72 are driven by motors 76and 78 or by a single motor and belt pulley system (not shown).

[0066] The accumulated dry polymer particles 80 in the bottom of tower12 cover the portal 82 out of the bottom reaction chamber 12 to maintainthe reduced pressure therein as first auger 68 moves the accumulatedpolymer particles 80 into bin 70. A shroud 84 covers first auger betweenreaction chamber 12 and bin 70 to prevent the influx of ambient air intoreaction chamber 12 and bin 70 is closed by a lid 86 at the top thereof.A portal 88 in the bottom of bin 70 allows the accumulated polymerparticles in bin 70 to be moved out of bin 70 into hopper 74. In thesame manner that the accumulated polymer particles 80 cover the portal82 in the bottom of reaction chamber 12, accumulated polymer particles90 cover the portal 88 in the bottom of bin 70 to prevent an influx ofambient air therethrough.

[0067] As will be explained below, the conditions under whichpolymerization and crosslinking occur are such that the particles ofpolymer 80 which accumulate at the bottom of reaction chamber 12 aresubstantially dry and have a low moisture content, and in light of theability of some polymers to absorb moisture, preventing access to theaccumulated polymer 80 by relatively humid ambient air is necessary topreventing the caking of the dry, accumulated polymer 80 as it is movedout of reaction chamber 12. Those skilled in the art who have thebenefit of the disclosure will recognize that other means can beutilized to remove the dry accumulated polymer 80 from the bottom ofreaction chamber 12 without breaking the vacuum therein. For instance,commercially available gravity feed, intermittent dump, and suctiondevices are all used to advantage for this purpose.

[0068] As shown in FIG. 2, feed line 20 enters reaction chamber 12 andterminates in a loop 94 having a plurality of nozzles 18 set therein.Alternatively, a single nozzle may be used. Nozzles 18 are preferablyscrewed into the threads 96 formed at intervals around the loop 94 forease in removing nozzles 18 for cleaning and/or changing. In anotherpreferred embodiment (not shown), the loop 94 in feed line 20 ispositioned outside of the top of tower 12. The latter embodiment isparticularly advantageous for frequent changing of nozzles 18 to, forinstance, change the diameter of the polymeric spheres.

[0069] If larger diameter particles are desired, the mixture in line 20is sprayed into reaction chamber 12 at relatively low pressure, e.g.,about 517 KPa to about 2.06 MPa through nozzles 18 having a largerdiameter orifice, for instance, a number 16 nozzle. If it is desired toproduce a smaller diameter sphere, the pressure in line 20 is increasedwith pump 40, e.g., from about 1.03 MPa on up to as high as perhaps 13.7MPa, causing the mixture to be atomized into finer sized particles. Ifeven smaller particles are desired, or if it is desired to producesmaller diameter particles at lower spray pressures, nozzles 18 arereplaced with nozzles having smaller orifices, e.g., a number 64 nozzle.

[0070] With reference to the figures, the method of continuouslyproducing a polymer in accordance with the present invention will now beexplained. The method comprises the mixing of the monomer source inwater or organic solvent in mixer 44 to prepare a liquid monomer source.Alternatively, liquid monomer sources may be obtained from sources knownto those skilled in the art. It is preferred that the monomer be anaqueous monomer source. An initiator, crosslinker, additional water,neutralizer and/or other reagents may be added to the monomer source inmixer 44. In the preferred embodiment of the process, the monomer,initiator, and other reagents used will be soluble in water or theorganic solvent used to prepare the liquid monomer source. It ispreferred, however, that the monomer, initiator and other reagents aresoluble in water. Initiator sources suitable for use with selectedmonomers will be known to those skilled in the art.

[0071] It is preferred that the initiator is added downstream from themonomer source immediately prior to the mixture being sprayed into thereaction chamber 12 to reduce the likelihood that line 20 or nozzles 18will become clogged by prepolymerization of the monomers. Although it ispreferred that an initiator be added to the monomer source, somemonomers may undergo self-initiated polymerization, thus eliminating theneed for an initiator. However, the rate and extent of polymerization isfacilitated by the use of an initiator.

[0072] Note that it may be advantageous to agitate or otherwise insureadequate mixing of initiator and aqueous mixture by use of a secondmixing means (not shown) similar to mixing means 44 downstream of thepoint at which the initiator is added to line 20.

[0073] Reaction chamber 12 is heated by heater 14 and the pressure ofthe atmosphere is controlled according to the monomer source beingpolymerized. Desired pressures at which to cause polymerization ofselected monomers will be known to those skilled in the art. Theatmosphere is maintained at a reduced pressure by vacuum pump 16. Theatmosphere may be controlled at a positive pressure by use of a pressurerelease valve in conjuction with the pressure evacuation pump. However,a positive pressure may be established by a pressure pump or other meansknown to those in the art in the chamber prior to spraying in themixture.

[0074] The mixture of monomers and/or reagents is sprayed into theheated, controlled atmosphere, thereby forming droplets of the mixture.The droplets are allowed to fall through the reaction chamber for aperiod of time sufficient to allow the desired degree of polymerizationof the monomers, and where a crosslinker has been added, crosslinking ofthe polymerized monomer, to form particles of polymer. The polymerparticles formed may be linear, branched or crosslinked polymers,depending upon the composition of the sprayed mixture.

[0075] As the droplets of the mixture of monomers and/or reagents fallfrom the spray nozzle through the chamber, water and/or solventsassociated with the polymerization mixture are continually evaporated orvolatilized as the polymerization reaction occurs. In the presence ofthe preferred reduced pressure within chamber 12, water and/or solventassociated with the mixture is continually evaporated or volatilized dueto both the presence of heat and the reduced pressure. Vapors areevacuated by vacuum pump 16 during the polymerization action.Alternatively, in the presence of positive pressure within chamber 12,the water and/or solvent associated with the mixture is evaporated dueto the heat within the chamber.

[0076] The polymer particles produced as a result of the polymerizationprocess are in the form of a substantially dry powder 80. The polymersproduced in dry particle form by this process may have a particle sizefrom as small as approximately 2 microns up to as large as about 125,000microns (approximately ⅛ inch). The size of the polymer will depend uponthe pressure, temperatures, and other parameters discussed more fullybelow which are present and/or utilized during the polymerizationprocess. The polymer size, shape, and density, however, will berelatively uniform when produced under similar conditions. The fallenparticles of polymer 80 which collect at the bottom of reaction chamber12 are removed while continuing to control the pressure within thechamber. The atmosphere will be maintained at the pressure desired forthe selected polymerization desired as the polymer is removed.

[0077] In a particularly preferred embodiment, the method of the presentinvention additionally comprises allowing sufficient fallen particles ofpolymer 80 to accumulate at the bottom of reaction chamber 12. Theaccumulated polymer particles form a large enough mass of heatedparticles to decrease the amount of energy required to maintain thetemperature of the atmosphere within reaction chamber 12 at a desiredtemperature.

[0078] It is preferred that the atmosphere in reaction chamber 12 beheated to a temperature of between about 23.8° C. and about 148.8° C.Temperatures of between about 82.2° C. and about 110° C. have been foundto be particularly preferred. Although it is possible to make polymersat temperatures below 37.8° C., a larger reduction of the pressurewithin reaction chamber 12 must be present if low water or solventcontent and low residual monomer levels are to be maintained.

[0079] The polymerization reaction and, when crosslinker is added to themixture, crosslinking which occurs as the droplets fall through reactionchamber 12 is exothermic such that relatively little external heat isneeded from heater 14 once a desired temperature is reached and thecontinuous polymerization/crosslinking is underway. Hence, temperaturesof well above, for instance, 37.8° C. can be maintained withoutcompromising the efficiency of the method. Further adding to theefficiency of the method of the present invention is the heat retentionof the accumulated mass of particles 80 at the bottom of reactionchamber 12.

[0080] The pressure of the atmosphere inside reaction chamber 12 neednot be reduced below or raised above ambient atmospheric pressure toproduce polymers. However, even relatively minor reductions in thepressure below nominal ambient pressure of about 101,580 N/m² causedisproportionate decreases in the water content of the polymers producedand the amount of unpolymerized residual monomer which does notparticipate in the polymerization and/or cross-linking reaction. Forthis reason it is preferred that the polymerization process be conductedunder reduced pressure conditions in the chamber.

[0081] Reductions in pressure of from about 338.6 up to about 50,790N/m² is preferred for use in connection with the method of the presentinvention. For a given particle size, the water and/or residual monomercontent is directly correlated between the temperature of the atmospherewithin reaction chamber 12 and the pressure at which the atmospherewithin reaction chamber 12 is maintained. As a general rule, astemperature is increased, the percentage of residual monomer and/orwater or solvent content can be maintained at low levels withprogressively smaller reductions in pressure relative to ambientpressure. Likewise, as the pressure of the atmosphere in reactionchamber 12 is decreased relative to ambient, low percentages of residualmonomer and/or water or solvent content can be maintained withprogressively lower temperatures.

[0082] Alternatively, the polymerization reaction may be conducted underincreased pressure conditions within reaction chamber 12. Increases inpressure within the reaction chamber of from about ambient to about 2psi may be used to practice the invention. As a general rule, astemperature is increased, the percentage of residual monomer and/orwater or solvent content can be maintained at desired low levels withprogressively smaller increases in pressure relative to below ambientpressures. Likewise, as the pressure of the atmosphere in reactionchamber 12 is increased relative to ambient, low percentages of residualmonomer and/or water or solvent content can be maintained withprogressively higher temperatures.

[0083] The shape of the polymer is also influenced by the below ambientpressure in the chamber. Varying the pressure allows production of fromspherical to more irregular-shaped polymers. At lower below ambientpressures, the polymers will be less uniform in shape and have rougheredges or flake-like appearances. As the reduced pressure approachesambient, the polymers become more spherical than is observed withpolymers produced, for example, at 15 inches of Hg below atmosphericambient pressure. Increasing the pressure within the chamber enables theproduction of a smoother, more dense polymer sphere than those producedin low atmospheric pressure conditions.

[0084] The period of time required during which the droplets fallthrough the atmosphere within reaction chamber 12, determine the heightof the reaction chamber. As a general rule, fall times of between about5 and about 60 seconds are required under the preferred conditions oftemperature and controlled pressure to achieve the desired degree ofpolymerization, crosslinking, and evacuation of water/solvent andresidual monomer for most monomer/crosslinker mixtures. Experimentationhas shown that reaction chamber height must be adequate to allowsufficient reaction chamber fall times in order to achieve the desiredextent of polymerization.

[0085] The period of time the droplet is allowed to fall throughreaction chamber 12 (and hence, the height of that chamber) is alsorelated in part to the diameter of the droplet sprayed from nozzle 18. Anozzle 18 having a large orifice 98 therein produces a larger diameterdroplet such that either the reaction chamber fall time of the dropletmay be increased, the reduction in the pressure of the atmosphere inreaction chamber 12 may be increased, the temperature may be increased,or some combination of changes in these three parameters may beeffected, in order to obtain the desired degree of polymerization, andwater/solvent evaporation throughout the resulting particle. In the caseof very large diameter droplets, pressure reductions of greater than67,720 N/m², temperatures of over 101.7° C., and reaction chamber falltimes in the 20 second or higher range may be required to allow thedesired degree of polymerization and evaporation of liquid.

[0086] Another variable affecting the production of polymers inaccordance with the method of the present invention is the pressure atwhich the mixture of monomer and initiator and/or crosslinker is sprayedinto the heated, controlled atmosphere in reaction chamber 12. Ingeneral, as the pressure at which the mixture is sprayed increases, thesize of the droplet decreases, requiring concomitant changes in eitherreaction chamber fall time, temperature, reduction in pressure inreaction chamber 12, the diameter of the orifice 98 in nozzle 18, orsome combination thereof. Satisfactory results have been obtained atspray pressures of between about 517 KPa and about 13.7 MPa, andpressures of between about 698.3 KPa and about 1.20 MPa represent aparticularly preferred embodiment of the method of the presentinvention. The pressure in the line at which the mixture is sprayed, aswell as the reduced temperature, prevent the polymerization of monomersprior to their being sprayed into the chamber. Therefore, thecombination of decreasing temperature in the feed line, increasingpressure in the feed line and introducing the initiator immediatelyprior to spraying the mixture into the chamber essentially eliminatesany prepolymerization of monomer in the feed line.

[0087] A final variable affecting the method of the present inventionand the various parameters of pressure, temperature and fall time atwhich the method is conducted is the nature of the monomer, initiator,crosslinker and other reagents desired to be polymerized. By referenceherein to a monomer, it is intended to refer to any organic moleculewhich is capable of being polymerized by covalent bonding to otherorganic molecules and/or itself to form chains. Many of the polymers canalso be crosslinked. Although it is not intended to limit the method ofthe present invention to only the following monomers, the followinglisting will provide an example of certain monomers, includingfunctionalized and/or unfunctionalized olefins, which may be polymerizedand in most cases crosslinked in accordance with the method of thepresent invention:

[0088] (a) water-soluble, ethylenically unsaturated monomers asdescribed in the above-incorporated Yamasaki, et al. U.S. Pat. No.4,446,261: acrylic acid, methacrylic acid, salts of acrylic acid andmethacrylic acid, acrylamide, methacrylamide, N-substituted acrylamides,N-substituted methacrylamide, 2-acryloylethane-sulfonic acid,2-methacryloylethane sulfonic acid, salts of 2-acryloylethane-sulfonicacid and 2-methacryloylethane-sulfonic acid, styrene-sulfonic acid,salts of styrene-sulfonic acid, 2-hydroxyethyl acrylate and2-hydroxyethylmethacrylate;

[0089] (b) the monomers described in Markus, U.S. Pat. No. 2,810,716:acrolein, allylidenediacetate, acrylonitrile, esters of acrylic andmethacrylic acid (including methyl methacrylate, ethyl methacrylate,fumaric acid, monomethylfumarate, dimethylfumarate, monoethylfumarte,diethylfumarte, maleic anhydride, maleic acid, monomethylmaleate,dimethylmaleate, monoethylmaleate, diethylmaleate,dimethylmethylenemalonate, diethylmethylene malonate, itaconic acid,monomethylitaconate, dimethyl itaconate, monoethyl itaconate,diethylitaconate, atrophic acid, methyl atropate, and ethyl atropate),chloracrylic acid and esters thereof, bromoacrylic acid and estersthereof, iodoacrylic acid and esters thereof, ortho-, meta-, andparamethylstyrene, fluorostyrene and chlorostyrene, a-sulfoacrylic acid,salts and esters, a-amino-acrylic acid, salts and esters, n-monomethyland N,N′-dimethyl acrylamide, acrylic and methacrylic anhydride,methylvinylketone, hydroxymethylvinylketone, ortho- andparamethoxystyrene, ethyleneglycol monomaleate, ethylglycolmonofumarate, N-vinylmethylacetamide, vinyl acetate, vinyl butyrate,vinyl benzoate, vinylquinoline, and vinylpyridines such as2-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine,2-vinyl-5-ethylpyridine, N-vinylpyrrolidone, cyclopentadiene,N-vinylphthalimide, N-vinylsuccinimide, N-vinylacetamide andN-vinyl-diacetamide;

[0090] (c) the monomers described in Glavis, et al., U.S. Pat. No.2,956,046: salts of unsaturated monomeric acids such as quaternaryammonium salts and amine salts thereof and salts of ammonia, alkalimetals and alkaline earth metals, includingB-hydroxyethyltrimethylammonium acrylate, benzyltrimethyl ammoniumacrylate, amine salts, monomethylammonium acrylate, and di- and tri-methylammonium acrylate;

[0091] (d) the monomers described in Wichterle, et al., U.S. Pat. No.3,220,960: dimethylaminoethyl methacrylate, piperidinoethylmethacrylate, morpholinoethyl methacrylate, methacrylylglycolic acid,methacrylic acid, monomethacrylates of glycol, glycerol and ployhydricalcohols, dialkylene glycols and polyalkylene glycols and thecorresponding acrylates;

[0092] (e) the monomers described in Bashaw, et al., U.S. Pat. No.3,229,769: cross-linked, substantially water-insoluble, water-swellablesulfonated alkaryl and aromatic polymers such as cross-linked polysodiumstyrene sulfonate and sulfonated polyvinyltoluene salts, copolymers ofsuch sulfonated alkaryl and aromatic materials with acrylonitriles,alkyl acrylonitriles, acrylates and methacrylates, cross-linkedpolyvinyl alcohol and polyacrylamide and crosslinked copolymers ofpolyacrylamide, e.g., of acrylamide and acrylic acid or acrylamide andmonovalent salts of acrylic acid, and cross-linked heterocyclic monomerssuch as polyvinyl morpholinone, poly-5-methyl-N-vinyl-2-oxazolidinone,and polyvinyl pyrrolidene;

[0093] (f) the monomers described in Assarsson, U.S. Pat. No. 3,664,343:water-insoluble hydrophilic poly (ethylene oxide) polymers made bysubjecting water-soluble poly (ethylene oxide) polymers to ionizingradiation (such polymers are homopolymers of ethylene oxide andcopolymers of ethylene oxide with one or more alkylene oxides such aspropylene oxide, styrene oxide, and 1,2-butylene, 2,3-butylene andisobutylene oxide, all as described in U.S. Pat. Nos. 3,127,371,3,214,387, 3,275,998, 3,275,199 and 3,399,149);

[0094] (g) the monomers described in Gross, et al., U.S. Pat. No.3,926,891: alkyl acrylates and methacrylates such as methyl acrylate,ethyl acrylate, propyl acrylate, hexyl acrylate, butyl methacrylate,hexyl methacrylate, octyl methacrylate, decyl methacrylate and omegahydroxy alkyl acrylates such as 2-hydroxyethyl acrylate, hydroxymethylacrylate, 3-hydroxypropyl acrylate and 4-hydroxybutyl acrylate;

[0095] (h) ethylene, 1,3-dienes, styrene, halogenated olefins, vinylesters, acrylates, methacrylates, acrylonitrile, methacrylonitrile,acrylamide, methacrylamide, N-vinyl carbazole, N-vinyl pyrrolidone,propylene, and

[0096] (i) alkenes, vinyl acetate.

[0097] It will be understood by those skilled in the art who have thebenefit of this disclosure that the references to a monomer throughoutthis specification and claims also contemplate the co-polymerization ofmonomers such as maleic acid and styrene to form commercially usefulco-polymers, graft polymers, block polymers. Examples of suchco-polymerizations can be found, for instance, at column 2, lines 66 et.seq. of U.S. Pat. No. 4,057,521. As is the case for the selection of aparticular combination of monomer, crosslinker and initiator forpolymerization and cross-linking in accordance with the method of thepresent invention, the selection of such combinations of monomers iswell known in the art and forms no part of the invention hereof suchthat further description of such co-polymerizations is unnecessary.

[0098] In the same manner that the method of the present invention isnot restricted with respect to the particular monomer or monomersutilized, a large number of crosslinkers are utilized to advantage. Suchcrosslinkers include any organic compound capable of reacting with anorganic polymer in aqueous solution and include, generally, compoundshaving at least two polymerizable double bonds, compounds having atleast one polymerizable double bond and at least one functional groupreactive with an acid-containing monomer or polymer, compounds having atleast two functional groups reactive with an acid-containing monomer orpolymer, and polyvalent metal compounds which are capable of formingionic cross-linkages. A non-limiting listing of a number of suchcrosslinkers includes:

[0099] polyvinyls, e.g., divinylbenzene, divinyltoluene, divinyl acidanhydrides, divinyl sulfone, divinyl benzene sulfonate, and their alkylor halogen-substituted products;

[0100] polyesters of unsaturated mono- or polycarboxylic acids withpolyols, e.g., ethylene glycol, trimethylol propane, glycerine, andpolyoxyethylene glycols;

[0101] bisacrylamides, e.g., N,N′-methylene-bisacrylamide andN,N′-methylenebismethacrylamide;

[0102] carbamyl esters obtained by reacting polyisocyanates withhydroxyl-group containing monomers;

[0103] di-, tri-, or tetraesters of acrylic or methacrylic acid;

[0104] polyallyl esters of polycarboxylic acids, e.g., diallyl phthalateand diallyl adipate;

[0105] esters of unsaturated mono- or polycarboxylic acids withmono-allyl esters of polyols, e.g., the acrylic acid of polyethyleneglycol monoallyl ether, allyl acrylate, diallyl ethylene glycol ether,and divinyl ether of ethylene tri- or diethylene glycol;

[0106] di- or triallylamine, N,N′-diallylacrylamide,diallylmethacrylamide;

[0107] N-methylol acrylamide, N-methyloylmethacrylamide;

[0108] glycidyl acrylate and methacrylate, polyethylene glycoldiacrylate, polyethylene glycol dimethacrylate;

[0109] substituted hexadienes such as2,5-dimethyl-3,4-dihydroxy-1,5-hexadiene and 2,5-dimethyl-2,4-hexadiene;

[0110] olefinically unsaturated mono- or polycarboxylic acids such asacrylic, methacrylic, crotonic, isocrotonic, angelic, tiglic, senecioic,maleic, fumaric, itaconic, aconitic, teraconic, citraconic, mesaconic,and glutaconic acid;

[0111] glyoxal;

[0112] polyols, e.g., ethylene glycol and polyhaloalkanols such as1,3-dichloroisopropanol and 1,3-dibromoisopropanol;

[0113] polyamines, e.g., alkylene diamines (ethylene diamine),polyalkylene polyamines, triethanolaminediacrylate and dimethacrylate,triethanolamine triacrylate and trimethacrylate, and diacrylate anddimethacrylate of bishydroxylacetamide;

[0114] polyepoxides and haloepoxyalkanes, e.g., epichlorhydrin,epibromohydrin, 2-methyl epichlorhydrin and epiiodohydrin;

[0115] polyglycidyl ethers and polyol polyglycidyl ethers such asethylene, diethylene, and propylene glycol diglycidyl ether, glycerintriglycidyl ether, glycerin diglycidyl ether and polyethylene glycoldiglycidyl ether, tartaric acid diacrylate and trimethacrylate,triethylene glycol diacrylate and dimethacrylate, ethylene glycoldimethacrylate and propylene glycol diacrylate;

[0116] oxides;

[0117] hydroxides;

[0118] weak acid salts (e.g., carbonate, acetate) of alkaline earthmetals (calcium, magnesium) and zinc, strontium and barium, e.g.,calcium oxide and zinc diacetate; and

[0119] polyvalent metal salts of acrylic acid and methacrylic acid.

[0120] Likewise, it is not intended that the method of the presentinvention be restricted with respect to the initiator utilized. Radicalscan be produced by a variety of thermal, photochemical, and redox(oxidative-reduction) methods known to those skilled in the art. Thebenefits of initiator selection are also known to those skilled in theart. Appropriate polymerization initiators well known in the artinclude:

[0121] peroxygen compounds (sodium, potassium and ammonium persulfate),hydrogen peroxide, caprylyl and benzol peroxide, cumene hydroperoxides,acetyl peroxide, tert-butyl diterphthlate, tertbutylperbenzoate, sodiumperacetate, tertbutylhydroperoxide, sodium percarbonate, andconventional redox initiator systems such as are formed by combining aperoxygen compound with a reducing agent such as sodium or ammoniumsulfite or bisulfite, L-ascorbic acid, or ferrous salts;

[0122] peroxides in combination with a reducing agent;

[0123] tetraphenylsuccinodinitrile,tetra-p-methoxyphenylsuccinodinitrile; and

[0124] azo initiators such as azobisisobutyronitrile (AIBN),4-t-butylazo-4′-cyano-4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis(2-amidino-propane)-hydrochloric acid salt.

[0125] It is also common to use mixtures of one or more of suchinitiators.

[0126] The present invention can be better understood by reference tothe following, non-limiting examples of cross-linked, water-absorbingpolymers produced in accordance with the method described above.

EXAMPLE 1

[0127] Aqueous solutions of the initiators sodium persulfate and2,2′-azobis (2-amidinopropane HCl (ABAH) (Polysciences, Inc.,Warrington, Pa.) and ascorbic acid were prepared in the followingproportions (all parts by weight): initiator water sodium persulfate0.650 12.346 ABAH 0.975 12.021 ascorbic acid 0.013 12.983

[0128] Other reagents were used in the following proportions: water29.70% acrylic acid (Catalog No. 42.61% 14723-0, Aldrich Chemical Co.,Milwaukee, WI) triallylamine (Catalog No. 0.30% T4500-4, AldrichChemical Co., Milwaukee, WI) caustic soda 22.12% ascorbic acid solution1.05% ABAH solution 2.11% sodium persulfate solution 2.11%

[0129] The water and acrylic acid were mixed while holding thetemperature at 10° C. and the triallylamine added. Caustic soda wasadded at a rate slow enough to hold the temperature under 40° C., thentemperature was brought down to 7° C. and held at that temperature asthe ascorbic acid and ABAH solutions were added. The resulting aqueousmixture was purged with nitrogen for 4 to 5 minutes and the sodiumpersulfate added. That mixture was mixed for 30 seconds at a temperatureunder 37.8° C. The mixture was then sprayed into a reaction chamberconstructed in accordance with the teachings of the present inventionthat was about 4.57 meters high with an atmospheric pressure therein ofabout 33,860 N/m² below ambient and which had been heated to about107.2° C. The resulting water-absorbing spherical particles were smoothsurfaced, ranged between about 50 to about 100 microns in diameter, andhad a water content of about 2%.

EXAMPLE 2

[0130] The method described in Example 1 was modified by using thefollowing proportions of reagents: water 26.00% acrylic acid (seeExample 1) 44.85% triallylamine (see Example 1) 0.31% caustic soda23.29% ascorbic acid solution 1.11% ABAH solution 2.22% sodiumpersulfate solution 2.22%

[0131] All process parameters were the same as in Example 1 except thatthe temperature of the reaction chamber 12 was 65.6° C. and the pressureof the atmosphere in the reaction chamber 12 was not reduced belowambient pressure. Although the resulting spherical particles were smoothsurfaced and capable of efficient water absorption, water content wasabout 8%. When repeated using potassium hydroxide in place of causticsoda, yield dropped by about 50%.

EXAMPLE 3

[0132] The method described in Example 1 was modified by omission of theinitiator ascorbic acid. The resulting smooth-surfaced sphericalparticles were obtained in approximately the same yield and size asobtained in Example 1, but water content was about 4%.

[0133] The polymerization process of the present invention produces adry powder-like particle, eliminating the need for drying, grinding,pulverizing and/or other methods to produce suitable for immediate usein the range of from about 2 to 125,000 microns in size. Moreover, thisinvention utilizes liquid monomer sources to produce a substantially drypolymer particle which does not rely upon a substrate on which toinitiate formation.

[0134] The process and apparatus described herein may also be used inthe continuous preparation of soaps and detergents. The raw materials ofsoap or detergent production are mixed and/or homogenized, and subjectedto treatments, as known to those skilled in the art to prepare a liquidmixture of soap- or detergent-making compounds. The liquid mixture isthen sprayed into the reaction chamber according to the abovedescription. Standard soap and detergent formulations known to thoseskilled in the art may be used to prepare a substantially dry powderedsoap or detergent.

[0135] The preparation of a soap or detergent will not require that thetemperature in the feed line of the above-described process andapparatus be reduced. The liquid mixture will however, be subjected topressure in the line and to the spraying and chamber conditionsdescribed above. Varying chamber pressure and temperature as describedabove will produce similar results in detergent and soap production asare obtained from monomer polymerization.

[0136] The process and apparatus described herein may also be used inthe preparation of several novel polymer products. Foremost, it has beenfound that by altering the operational parameters of the apparatus, notonly is the size and density of the product varied, but the shape andphysical properties of the products are varied as well. Moreparticularly, when the apparatus is operated at lower pressures andhigher temperatures, the water or other solvent in the mixture dropletsis violently released during polymerization. The result is asubstantially dry polymer product which has a puffed out irregular shapenot unlike cooked popcorn. The novelty of this product is believed to bein its irregular puffed shape, its low density, and in the case of thewater absorbing polymers, an enhanced ability to absorb water or urinedue to an increase in the polymer's surface area. Further, a productwith these characteristics is obtained without spray drying oradditional processing as is required in the known processes forobtaining similar products.

[0137] Similar known products do not have the same degree ofirregularity in their shape as they are most commonly formed through themechanical processes of pulverizing and chopping a mass of polymermaterial. Thus, known irregularly shaped polymers have less surface areaand commonly have higher densities. Known methods for obtainingirregularly shaped polymer products are described in U.S. Pat. No. Re.32,649 entitled “Hydrogel-Forming Polymer Compositions For Use inAbsorbent Structures,” reissued to Brandt et al. on Apr. 19, 1988 andU.S. Pat. No. 4,625,001 entitled “Method for Continuous Production OfCross-Linked Polymer” issued to Tsubakimoto et al. on Nov. 25, 1986.These patents are incorporated herein by reference.

[0138] An additional novel product is obtained from the process andapparatus described herein in the form of a substantially dry pigmentedcopolymer product for use in powder coating techniques. To obtain thisproduct the process further comprises the steps of adding a secondmonomer to the first mixture and the step of adding a pigment to thefirst mixture. The homogenized mixture is then sprayed into theapparatus forming mixture droplets which polymerize during free fall.The product obtained from this process is a substantially dry, pigmentedcopolymer that is radiation curable for use in powder coatingapplications; additional chemical or mechanical processing of thecopolymer product is not required.

[0139] The production of copolymers for use as binders in powdercoatings is described in U.S. Pat. No. 5,484,850 entitled “CopolymersCrosslinkable By A Free Radical Method” issued to Kempter et al. on Jan.16, 1996. This patents is incorporated herein by reference. As describedin the Kempter patent, copolymers for use in powder coatings typicallyrequire several manufacturing steps in their production. The monomerreagents are first polymerized into a copolymer. The copolymer is thendispersed or dissolved in an emulsion or solution in order to introduceadditives by various known techniques. Lastly, the copolymer compositionis dried in a conventional manner. A substantially dry, coloredcopolymer is formed from a homogenized mixture of monomers and variousadditives in a single step in the process and apparatus describedherein.

[0140] The term “controlled atmosphere” as used herein describes theinternal condition of the apparatus and the reaction conditions of thepolymerization process. As such, “controlled atmosphere” refers to anatmosphere that is substantially static. Any currents or movement ofgases within the apparatus or in the vicinity of where thepolymerization process is being carried out should be minimized; thereshould be no currents or turbulence present to interfere with the freefall of the polymerizing droplets. While the droplets are generallydescribed as falling through the apparatus, they are more accuratelydescribed as experiencing a free fall, which is preferably influencedonly by the force of gravity.

[0141] Those skilled in the art who have the benefit of this disclosurewill recognize that the above examples are set out by way ofexemplification and for the purpose of complying with the requirementsof the Patent Statute, and that those examples are not intended to limitthe scope of the present invention. Likewise, with respect to theapparatus 10, it will be recognized that changes can be made to theindividual structural elements comprising that apparatus withoutchanging the manner in which those elements function to achieve theintended result thereof. All such changes are intended to fall withinthe scope of the following claims.

What is claimed is:
 1. A polymerization apparatus comprising: a reactionchamber; means for heating said reaction chamber; means for controllingthe pressure within said reaction chamber; one or more nozzles connectedto a feed line for receiving a mixture of a monomer source and aninitiator source; and means for spraying the mixture into the topsection of the reaction chamber such that said spraying results in theformation of droplets of said mixture which experience free fall throughthe reaction chamber for a sufficient period of time to obtain a desireddegree of polymerization.
 2. The apparatus as set forth in claim 1,further comprising a means for removing the polymer from the bottom ofsaid reaction chamber while maintaining the heat and the pressure withinthe chamber.
 3. The apparatus as set forth in claim 2, wherein the meansfor removing the polymer comprises a trough located in the bottom of thereaction chamber, a first auger mounted in the bottom of said trough formoving the polymer out of the chamber, a bin into which said first augerdeposits the polymer and a second auger mounted in the bottom of saidbin for moving the polymer out of said bin.
 4. The apparatus as setforth in any one of the preceding claims, further comprising a means forcontrolling the temperature of the monomer and initiator mixture in saidfeed line.
 5. The apparatus as set forth in any one of the precedingclaims, further comprising a means for mixing the monomer and initiatorbefore the mixture of monomer and initiator is sprayed from saidnozzles.
 6. The apparatus as set forth in any one of the precedingclaims, further comprising a means for removing unpolymerized monomerfrom said reaction chamber.
 7. The apparatus as set forth in any one ofthe preceding claims, further comprising a means for purging the mixturein said feed line.
 8. The apparatus as set forth in claim 7, wherein thefeed line purging means comprise means to purge the feed line withnitrogen.
 9. The apparatus as set forth in any one of the precedingclaims, further comprising a means for purging said reaction chamber.10. The apparatus as set forth in claim 9, wherein reaction chamberpurging means comprise means to purge the reaction chamber withnitrogen.
 11. The apparatus as set forth in any one of the precedingclaims, wherein said reaction chamber is from about 3.65 meters inheight to about 30.48 meters in height.
 12. The apparatus as set forthin any one of the preceding claims, further comprising a separatereservoir for said monomer source and said initiator source.
 13. Theapparatus as set forth in claim 12, further comprising a reservoir for acrosslinker source.
 14. The apparatus as set forth in claim 13, whereinsaid crosslinker source is connected to means adapted to add crosslinkersource to said mixture of monomer source and initiator source prior tothe mixture being sprayed into said reaction chamber.
 15. The apparatusas set forth in any one of the preceding claims, wherein the mixture issprayed into said reaction chamber at from about 517 KPa to about 13.7MPa of pressure.
 16. The apparatus as set forth in any one of thepreceding claims, wherein means are provided to maintain the pressure inthe reaction chamber at less than ambient pressure.
 17. The apparatus asset forth in claim 16, wherein said means maintain the pressure in thereaction chamber at a pressure of from about 338.6 to about 50,790 N/m²below ambient pressure.
 18. The apparatus as set forth in any one of thepreceding claims, wherein said reaction chamber is heated to atemperature of from about 23.8° C. to about 176.7° C.
 19. The apparatusaccording to any of the preceding claims, wherein means are provided toincrease or decrease the size of each nozzle opening.
 20. The apparatusas set forth in any one of claims 1 to 18, wherein, in use, the monomersource is a functionalized or an unfunctionalized olefin.
 21. Theapparatus as set forth in any one of claims 1 to 18, wherein, in use themonomer source is acrylic acid.
 22. The apparatus as set forth in anyone of claims 1 to 18, wherein, in use, said monomer source is selectedfrom the group of compounds consisting of ethylenes, dienes, styrenes,propylenes, vinyls, acrylates, methacrylates, acrylonitrile,methacrylonitrile, acrylamide, methacrylamide, and alkenes.
 23. Anapparatus for continuous production of a detergent comprising: areaction chamber; means for heating said reaction chamber; means forcontrolling the pressure within said reaction chamber; one or morenozzles connected to a feed line for receiving a mixture of a detergentraw materials; and means for spraying the mixture into the top sectionof the reaction chamber such that said spraying results in the formationof droplets of said mixture which experience free fall through thereaction chamber for a sufficient period of time to obtain asubstantially dry detergent powder.
 24. A polymerization processcomprising the steps of: (a) preparing a first mixture of at least onemonomer source and a solvent selected from the group consisting ofwater, organic solvents and mixtures thereof; (b) adding an initiatorsource to the first mixture to form a second mixture; (c) spraying thesecond mixture into a heated, pressure controlled, substantially staticatmosphere, said spraying resulting in the formation of droplets of saidsecond mixture; and (d) allowing said droplets of the sprayed secondmixture to fall through the heated, substantially static atmosphere fora period of time sufficient to obtain a desired degree ofpolymerization.
 25. The polymerization process as set forth in claim 24,wherein the heated, substantially static atmosphere is maintained in aclosed vessel, or reaction chamber.
 26. The polymerization process asset forth in claim 25, wherein said second mixture is sprayed in at thetop section of the vessel, or reaction chamber.
 27. The polymerizationprocess as set forth in claim 25 or 26, wherein said vessel reactionchamber is about 3.65 to 30.48 meters in height.
 28. The polymerizationprocess as set forth in any one of claims 24 to 27, wherein said secondmixture is sprayed into the atmosphere through one or more nozzles. 29.The polymerization process as set forth in any one of claims 24 to 28,wherein the size of the polymer particle produced is selected byincreasing or decreasing the size of the nozzle opening.
 30. Thepolymerization process as set forth in any one of claims 24 to 29, whichfurther comprises adding a neutralizer to the first mixture.
 31. Thepolymerization process as set forth in any one of claims 24 to 30,wherein said solvent is continuously evacuated from the atmosphereduring the polymerization process.
 32. The polymerization process as setforth in any one of claims 24 to 31, wherein a substantially dry polymerpowder is formed as a result of the polymerization process.
 33. Thepolymerization process as set forth in claim 32, wherein the dry polymerpowder is recovered while maintaining a heated, substantially staticatmosphere.
 34. The polymerization process as set forth in claim 32 or33, wherein the dry polymer powder produced comprises a water-absorbingpolymer.
 35. The polymerization process as set forth in claim 32 or 33,wherein the dry polymer powder produced comprises a polymer suitable foruse as a powder coating.
 36. The polymerization process as set forth inclaim 32 or 33, wherein the dry polymer powder produced comprises anirregularly puffed shaped polymer having relatively low density.
 37. Thepolymerization process as set forth in any one of claims 24 to 37,wherein said atmosphere is at a temperature of from about 23.8° C. andto about 176.7° C.
 38. The polymerization process as set forth in anyone of claims 24 to 37, wherein said substantially static atmosphere isat reduced pressure.
 39. The polymerization process as set forth in anyone of claims 24 to 38, wherein said substantially static atmosphere isat positive pressure.
 40. The polymerization process as set forth inclaim 38, wherein said heated, substantially static controlledatmosphere is maintained at a pressure of from about 388.6 to about50,790 N/m² below ambient pressure.
 41. The polymerization process asset forth in any one of claims 24 to 40, wherein said second mixture issprayed into the heated, substantially static atmosphere at a pressureof between about 517 KPa and about 13.7 MPa.
 42. The polymerizationprocess as set forth in any one of claims 24 to 41, wherein the monomersource is an aqueous solution of a monomer and the solvent is water. 43.The polymerization process as set forth in any one of claims 24 to 41,wherein the monomer source is an aqueous emulsion of a selected monomerand the solvent is water.
 44. The polymerization process as set forth inany one of claims 24 to 43, wherein said first mixture is cooled priorto adding the initiator source.
 45. The polymerization process as setforth in any one of claims 24 to 44, which further comprises adding acrosslinker to the first mixture.
 46. The polymerization process as setforth in claim 45, wherein the crosslinker source is an aqueous solutionof a selected crosslinker and the solvent is water.
 47. Thepolymerization process as set forth in claim 45, wherein the crosslinkersource is an aqueous emulsion of a selected crosslinker and the solventis water.
 48. The polymerization process as set forth in one of claims24 to 47, wherein the monomer source is a water-soluble, unsaturatedmonomer.
 49. The polymerization process as set forth in any one ofclaims 24 to 48, wherein the monomer source is an unfunctionalizedolefin.
 50. The polymerization process as set forth in any one of claims24 to 48, wherein the monomer source is a functionalized olefin.
 51. Thepolymerization process as set forth in any one of claims 24 to 48,wherein the monomer source is acrylic acid.
 52. The polymerizationprocess as set forth in any one of claims 24 to 48, wherein said monomersource is selected from the group consisting of ethylenes, dienes,styrenes, propylenes, vinyls, acrylates, methacrylates, acrylonitrile,methacrylonitrile, acrylamide, methacrylamide, and alkenes.
 53. Thepolymerization process as set forth in any one of claims 24 to 47wherein the first mixture is cooled prior to adding the initiatorsource.
 54. The polymerization process as set forth in any one of claims24 to 53 which further comprises adding a neutralizer to the firstmixture.
 55. The polymerization process as set forth in any one ofclaims 24 to 54 wherein the second mixture is maintained at atemperature between about 26.6 degrees C. and about 93.3 degrees C. 56.A polymerization process for producing an acrylic acid containingpolymer comprising the steps of: (a) preparing an aqueous mixture ofpartially neutralized acrylic acid; (b) adding a polymerizationinitiator to the aqueous mixture to form a second mixture; and (c)spraying said second mixture into a heated, pressure controlled,substantially static atmosphere, said spraying resulting in theformation of droplets of said second mixture; and (d) allowing saiddroplets of the sprayed second mixture to fall through the heated,substantially static atmosphere for a sufficient period of time toobtain a desired degree of polymerization and thus form a partiallyneutralized acrylic acid containing polymer in particle powder form. 57.A process for the continuous preparation of a copolymer for use as apowder coating comprising the steps of: (a) preparing a liquid mixtureof two or more monomers; (b) homogenizing a pigment with the liquidmixture of monomers; (c) spraying the liquid mixture into a heated,pressure controlled, substantially static atmosphere, said sprayingresulting in the formation of droplets of the mixture; and (d) allowingsaid droplets of the sprayed mixture to fall through the heated,substantially static atmosphere a period of time sufficient to obtain asubstantially dry copolymer that may be used for powder coatingapplications.
 58. A process for the continuous preparation of anirregularly puffed shaped polymer comprising the steps of: (a) preparinga liquid mixture of one or more monomers; (b) spraying the liquidmixture into a heated, pressure controlled, substantially staticatmosphere having reduced pressure, said spraying resulting in theformation of droplets of the mixture; (c) allowing said droplets of thesprayed mixture to fall through the heated, substantially staticatmosphere a period of time sufficient to obtain a substantially dryirregularly puffed shaped polymer having relatively low density.
 59. Aprocess for the continuous preparation of a detergent comprising thesteps of: (a) preparing a liquid mixture of detergent raw materials; (b)spraying the liquid mixture into a heated, pressure controlled,substantially static atmosphere, said spraying resulting in theformation of droplets of the mixture; and (c) allowing said droplets ofthe sprayed mixture to fall through the heated, substantially staticatmosphere a period of time sufficient to obtain a substantially drydetergent powder.
 60. The polymer product produced by the process of anyone of claims 24 to
 58. 61. An acrylic acid containing polymer producedby an aqueous radical polymerization process comprising the steps of:(a) preparing an aqueous mixture of partially neutralized acrylic acid;(b) adding a polymerization initiator to the aqueous mixture to form asecond mixture of polymerization reagents; (c) spraying said secondmixture into a heated, substantially static atmosphere, said sprayingresulting in the formation of droplets of said second mixture; and (d)allowing said droplets of the sprayed second mixture to fall through theheated, substantially static atmosphere for a period of time sufficientto obtain a desired degree of polymerization and thus form a partiallyneutralized acrylic acid containing polymer in particle powder form. 62.The polymer as set forth in claim 61, wherein said polymer produced is awater-absorbing polymer.
 63. The polymer as set forth in claim 61,wherein said polymer produced is a copolymer may be used for powdercoating applications.
 64. The polymer as set forth in claim 61, whereinsaid polymer produced is an irregularly puffed shaped polymer havingrelatively low density.
 65. The polymer as set forth in any one ofclaims 61 through 64, wherein said polymer is produced in particlepowder form and has a particle size of less than approximately 100microns.